Known examples of strain wave gearing device units include units incorporating a cup-shaped flexible externally toothed gear as described in Patent Document 1. In such strain wave gearing device units, a rigid internally toothed gear is formed in an inner peripheral area of a cylindrical housing, and the cup-shaped flexible externally toothed gear is disposed inside the rigid internally toothed gear. An output flange is fixed in a coaxial manner to a boss defining the cup-bottom-surface portion of the flexible externally toothed gear.
To utilize a strain wave gearing device unit, a user attaches a motor shaft to an input-side wave generator, and attaches a driven member to the output-side end surface of the output flange. The high-speed rotation inputted to the wave generator from the motor shaft is delivered from the output flange as a reduced-rotation output. The driven member attached to the output flange is driven by the reduced rotation output.